OFDM
Orthogonal frequency-division multiplexing (OFDM) is frequently used to mitigate multi-path interference in a physical layer (PHY) of channels of wireless communication networks. Therefore, OFDM is specified for a number of wireless communications standards, e.g., IEEE 802.11a/g, and IEEE 802.16/16e, “IEEE Standard for Local and Metropolitan Area Networks—Part 16: Air Interface for Fixed Broadband Wireless Access systems,” IEEE Computer Society and the IEEE Microwave Theory and Techniques Society, October 2004, and “IEEE Standard for Local and Metropolitan Area Networks—Part 16: Air Interface for Fixed Broadband Wireless Access Systems, Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands,” IEEE Computer Society and the IEEE Microwave Theory and Techniques Society, February 2006, both incorporated herein by reference.
OFDMA
Based on the OFDM, orthogonal frequency division multiple access (OFDMA) has been developed. With OFDMA a separate sets of orthogonal tones (frequencies) are allocated to multiple transceivers (users) so that these transceivers can engage in parallel communication. For an example, the IEEE 802.16/16e standard has adopted OFDMA as the multiple channel access mechanism for non-line-of sight (NLOS) communications in frequency bands below 11 GHz.
HARQ
Hybrid automatic repeat-request (HARQ) operations can be used for error control in wireless networks. With HARQ, the receiver detects an error in a message and automatically requests a retransmission of the message from the transmitter. In response to receiving the HARQ, the transmitter retransmits the message until it is received correctly, unless the error persists. In one variation, HARQ combines forward error correction (FEC) with an error-correction code.
HARQ operation requires support at both the PHY and link level, i.e., layer 1 and 2 in the OSI protocol model, to provide a desired reliability on the wireless channels. Many existing wireless systems have adopted HARQ to deal with adverse wireless channels and improve reliability. For example, HARQ is used as an optional feature in the IEEE 802.16e standard for the OFDMA PHY.
However, an ambiguity can arise when the HARQ protocol, as defined in the current IEEE 802.16e standard, is applied on concatenated MAC protocol data units (MPDU). In addition, conventional HARQ unexpectedly prevents the wireless channel resources from being fully utilized. This is a serious problem for relay channels in mobile multihop relay networks, or next generation advanced IEEE 802.16 networks, as high capacity is one of the requirements for such networks.
To address these problems, new protocols are required.
For sake of clarify and brevity, some terminologies and acronyms are defined herein as follows.
Subscriber station (SS): a generalized equipment set providing connectivity between subscriber equipment and a base station (BS).
Mobile station (MS): a station in mobile service intended to be used while in motion or during halts at unspecified points. An MS is always a subscriber station (SS) unless specifically expected otherwise in the standard.
Relay station (RS): a station that conforms to the IEEE Std 802.16j standard and whose functions are 1) to relay data and possibly control information between other stations, and 2) to execute processes that indirectly support mobile multihop relay, see “Harmonized definitions and terminology for IEEE 802.16j Mobile Multihop Relay,” IEEE 802.16j-06/014rl, October 2006, incorporated herein by reference.
Protocol data unit (PDU): a set of data specified in a protocol of a given layer and including protocol control information of that layer, and possibly user data of that layer, see W. Stallings, “Data and Computer Communications”, Seventh edition, Prentice Hall, 2003, incorporated herein by reference.
Service data unit (SDU): the protocol data unit of a certain protocol layer that includes the service data unit coming from the higher layer and the protocol control information of that layer.